An apparatus for signal and/or current transmission between terminals which can move in relation to one another and which are fitted, on the one hand, on a fixed stator and, on the other hand, on a rotor of a cassette that can rotate about a common axis with the stator, in the case of which apparatus at least one flat ribbon cable, which is equipped with electrical conductors, runs in turns and forms a wound body, is arranged within the cassette between the terminals, and in the case of which apparatus the ends of the flat ribbon cable are connected to contact parts for the purpose of connecting ongoing cables.
Such an apparatus is required, for example, for transmitting a signal for the purpose of triggering the “airbag” of an impact protection system for motor vehicles. It is accommodated in the steering wheel of a motor vehicle for the purpose of transmitting electrical signals but also electrical current. With such an apparatus it is possible for the signal and/or current transmission to take place between fixed and moving parts of the motor vehicle without any sliding-action contacts or sliprings. Instead of the words “flat ribbon cable”, the abbreviation “FRC” will be used below.
EP 0 417 350 A1 has disclosed an apparatus for contactless current transmission between two terminals by means of an FRC wound in the manner of a spring barrel to form a wound body. In the case of a relative rotary movement between the two terminals connected by means of the FRC, the wound-on FRC “breathes” like the spring of a clock. The turns of the wound FRC are compressed in one direction of rotation to a smaller diameter. In the other direction of rotation, they open out to a larger diameter again.
An apparatus corresponding to the apparatus in accordance with EP 0 417 350 A1 is described in DE 195 11 693 A1. This document concerns a swivel connector, which is referred to as a steering column switch with a volute spring. The volute spring represents a connecting line which is wound on in the form of a cylinder. The stator of this swivel connector is formed by the switch housing itself, in which a lid chamber is formed. An open ring chamber, which represents the rotor and in which the volute spring is arranged, is used as the lid for the lid chamber.
DE 37 32 124 A1 describes an apparatus in the case of which the wound body comprises an FRC which is wound in the form of a bifilar coil. The length of the FRC arranged in the bifilar coil may be shorter than an arrangement with an FRC wound in the manner of a spring barrel.
EP 0 735 631 B1 describes an apparatus for connecting two terminals which can rotate in relation to one another, in the case of which apparatus the wound body is split into two subwindings with an opposite winding sense and a U-shaped reversal point, between which an annular guide body is arranged. The guide body is used for guiding and mutually supporting the subwindings.
The apparatus described in EP 0 556 779 B1 likewise has a cassette comprising a stator and a rotor. It does not have a separate guide body for the subwindings. In the case of this apparatus, these subwindings are formed by a plurality of FRCs, which overall form a wound body and each of which is arranged with a U-shaped reversal point in the cassette of the apparatus. The FRCs are designed to be elastic, and the regions of their reversal points are so stable that the turns of the FRC are pressed in the direction of the stator on one side and the rotor on the other side. In the event of a rotation of a steering wheel of a vehicle equipped with such a cassette, all of the reversal points move in the circumferential direction of the cassette.